This invention relates generally to medical diagnostic instruments, and has particular reference to an ophthalmoscope having a novel lens shifting mechanism.
In most prior art ophthalmoscopes there is a single lens disc that can be manually rotated to bring a selected one of a plurality of lenses into registry with the physician's viewing path through the instrument. Each lens has a different diopter and the physician will have as many diopter choices as there are lenses in a particular lens disc. By way of example, the applicant is aware of a commercially available ophthalmoscope having a disc with sixteen lenses and another that has a twenty-four lens disc.
It may be desirable to have a still greater choice of different lens diopters and to this end some instruments have been developed in the past that employ two lens discs, the lenses of the two discs being used in combination to increase the number of different lens diopters as where one disc acts as a "multiplier". In these instruments, to the best of applicant's knowledge, there are no automatic lens shifting mechanisms as in the present invention. The applicant is aware of an ophthalmoscope manufactured by American Optical of Southbridge, Mass. that employs two lens discs that are interconnected by a Geneva movement. However, the applicant does not know of any patent that is directed to this construction or to a construction as disclosed herein where a cam mechanism is utilized to provide an automatic lens shifting means for a pair of lens discs.